1) Field of the Invention
The present invention relates to a charge-exchange device.
Development of powerful next-generation neutron sources is receiving general attention as a target for the development of advanced new scientific technology in the 21st century. One such project is the realization of a large-scale proton accelerator in the order of 5 MW by NSNS in U.S.A and by ESS in Europe. A proposal is also being made following the neutron study plan of the Japan Atomic Energy Research Institute to establish a multi-purpose research facility for utilizing proton beams in the order of 1.5 GeV, 8 MW with an ultra powerful super conducting linear proton accelerator as the principal facility. A storage ring for generating a very intense pulsed neutron (equivalent to 5 MW) is required for the study of neutron scattering which is one of the principal study themes. Since these accelerators and storage rings generate neutron beams having a large output which has not been experienced in the past, counter measures against leakage of beams from not only the accelerators themselves but also peripheral facilities, as well as a reduction in radio activation are deemed to be of critical importance in attaining stable and safe operation of accelerators and storage rings. Therefore, success of the countermeasures against reduction of radio activation is understood to be a decisive factor for the good result of the development and easiness of maintenance and operation.
The injection and ejection device for the storage ring is adapted to receive an H.sup.- beam of 1.5 GeV (.beta.=0.92) having a peak of 30 mA for a period of 3.6 ms from the super-conducting linear accelerator and to store the same in the ring as an H.sup.+ beam at one time, and after having compressed it to a beam in the order of 0.5 .mu.s, and to deliver the beam to the target which will be the neutron source in the form of a pulse of 50 Hz having a peak of 100 A.
The present invention relates to a charge-exchange device particularly suitable for use with an injection device for a storage ring for generating a very intense pulsed neutron beam as described above.
2) Prior Art
It is conventional practice to use an electromagnet for changing the trajectory of a proton beam and the like and a foil for exchanging a charge for injection into such a ring (see for example A. H Mohagheghi et al. "Interaction of relativistic H.sup.- ions with thin foils" PHYSICAL REVIEW A, Volume 43, Number 3, Feb. 1, 1991 (published by The American Society)). However, in order to take advantage of a super-conducting linear accelerator as included in the above-mentioned plan, it is expedient that by expanding the pulse width the output is made larger as compared to a normal conducting accelerator while the beam current is kept low, so that any adverse affect of the space charge over the beam is minimized. Accordingly, it becomes necessary for a multi-turn injection of some thousands pulses to be conducted for a period in the order of 3.6 ms so as to store a sufficient beam in the ring.
In this instance, it should be noted that since the foil will be exposed to radiation by the particles themselves which have been injected for a long period of time and the proton beam which has previously been injected and is circulating around the ring will collide against the foil again resulting in damage to the foil, it is difficult to keep the foil in a sound condition. Besides, it is also pointed out that the peripheral devices will be subjected to radio activation due to the variation of the trajectory and scattering of the proton beam. In other words, the beam injection device which includes a charge-exchange device as one of the components is a device in which it is most difficult to take countermeasures against radio activation among such components as constitute the ring. Therefore, it is urgently required to develop a novel apparatus to overcome these problems.
In view of this situation, the inventor of the present application has conducted studies as reported in the research report of the Japan Atomic Energy Research Institute as titled JAERI-Research 97-040 (June, 1997), a novel method of injection and ejection wherein an H.sup.- beam which has been accelerated by a super-conducting linear accelerator is charge-exchanged and injected into and ejected from the storage ring as proton beams. In addition, the inventor has studied many other methods using electrons, ionsand photons. It has been demonstrated that among many methods that have been studied, the method of colliding the beam against the plasma ion in the Lorentz field created by interaction of the strong wiggler magnetic field and high energy particles and the method of light excitation by Doppler-shifted photon beam are regarded as the most promising methods.
The inventor of the present application proposed another method of injecting the beam into the storage ring in the research report of the Japan Atomic Energy Research Institute titled JAERI-Research 96-041 (June, 1997). The injection device according to this method is constructed by a neutralizer and an ionizer. The neutralizer is located at the beam transport port section outside of the ring and consists of an electromagnet for convergence and a wiggler and is adapted to neutralize H.sup.- to H.sup.0. The ionizer is located at the linear section of the ring and consists of a wiggler and an optical resonator. The ionizer is adapted to utilize the Lorentz force owing to the wiggler magnetic field and the relativistic velocity of the injected particles to ionize the H.sup.0 beam by scattering it to the photon beam. According to this method of injection, the trajectory of the beam in the ring will not be varied by a bump electromagnet in the prior art apparatus, or beam scattering by the foil will not be caused. However, it has to be pointed out that although the countermeasure against low radio activation in the beam loss at the injection part of the proton storage ring is the greatest technical problem, such technical problems are not being considered currently.
The inventor of the present application also proposed in the research report of the Japan Atomic Energy Research Institute titled JAERI-Research 97-057 (August, 1997) another method of injecting the beam into the storage ring. According to this method, utilization of Lorentz electric field of the injected particles having a relativistic velocity by the neutralizer and the ionizer is the same as that of said another injection method, as described in the above-mentioned research report titled JAERI-Research 97-041, while the manner of ionization is different and the charge is exchanged efficiently by making use of a Doppler effect and the resonance absorption of laser beam. To reduce radio activation, or in order to reduce radio activation caused by beam spill, the beam deflection angle by the wiggler magnetic field is made smaller so that the range in which the magnetic field is present is shortened. However, as a consequence, the output of the laser must be increased to the extent that it becomes impractical.